(1) Field of the Invention
The present invention relates to a wafer positioning apparatus which is used in a working process of semiconductor wafers for positioning a wafer with respect to a notched portion (orientation flat or notch) formed on a part of the wafer.
(2) Prior Art
When semiconductor wafers are worked or measured, the wafers are usually enclosed in a shelf-shaped cassette and then taken one after another out of the cassette by a carrier system and held on a stage of a processor. Since position of a notched portion of the wafer within the cassette is random and the positioning in the processor is performed with respect to the notched portion at the edge portion of the wafer, the wafer must be held on the stage so that the notched portion is at a definite position (for example, a definite position in front of the stage).
Therefore the wafer taken out of the cassette is once held on the positioning apparatus by the carrier system and transferred to the correct position with respect to the notched portion of the wafer and then held on the stage of the processor.
A wafer positioning apparatus used in such process in the prior art usually has structure that a wafer is rotatably supported and a rubber roller abuts on a peripheral portion of the wafer and is rotationally driven thereby the wafer is rotated, and when a notched portion of the wafer attains to a portion of the rubber roller or a portion of a photosensor or the like, the rotation of the wafer is stopped and the positioning is performed (for example, refer to Japanese patent application laid-open No. 16984/1979).
Consequently, when the wafer is positioned, the peripheral portion of the wafer is pushed and rotated by the rubber roller or is contacted with other member and is moved, thereby the peripheral portion of the weak wafer may be broken.
The present inventors have proposed a silicon wafer positioning apparatus in U.S. Pat. No. 4,770,600. Also in this apparatus, the positioning is performed in that both sides of a wafer are held and supported on a supporter and the end of the wafer is pushed by a movable weight and moved to the inside. Consequently, a wafer positioning apparatus to enable the positioning without touching the peripheral portion of the wafer has been desired.